1. Field of the Invention
The present invention relates to a semantic search system based on semantic relationship information between resources described on an ontology and, particularly, to a search technique that ranks resources by using a relevance scoring function reflecting the number of meaningful semantic paths between resources and keywords, the coverage of keywords, and the distinguishability of keywords related to the resources, and provides ranked resources to users. More particularly, the present invention relates to a semantic search technique capable of automatically weighting various semantic relationships between resources without the intervention of an expert, thus effectively utilizing the present invention, irrespective of the complexity and size of ontology, and effectively handling queries consisting of one or more keywords with different importance.
2. Description of the Related Art
Currently, a keyword-based search, a search scheme provided by a search engine, basically ranks query results according to whether or not a resource as a search subject (or search target) has a keyword and the number of keywords included in the resource, and provides ranked query results to a user. In this case, the accuracy of the search results is very low since the keyword-based search is ignorant of the type of resources and the semantic relationships between the resources and keywords. In an effort to solve this problem, a semantic search utilizing ontology clarifying a semantic relationship between a type of resource and a resource has been proposed.
The related art of the semantic search includes N. Stojanovic, R. Studer, and K. Stojanovic, “An Approach for the Ranking of Query Results in the Semantic Web,” published in the Proc. of ISWC, pages 500-516, October 2003 (referred to as a ‘relevant research 1’, hereinafter), and C. Rocha, D. Schwabe, and M. P. de Aragao, “A Hybrid Approach for Searching in the Semantic Web,” published in the Proc. of WWW, pages 374-383, 2004 (referred to as a ‘relevant research 2’, hereinafter).
The relevant researches 1 and 2, propose a ranking scheme based on semantic relationship information between the resources described in ontology, in order to enhance the accuracy of a semantic search. In the ranking scheme proposed in the relevant researches 1 and 2, the ranks of search target resources are determined in consideration of the amount of semantic relationships between resources and the specificity of the semantic relationships through a link analysis of the ontology. Because this scheme takes the semantic relations between a keyword and a resource into consideration in performing a search, the accuracy is improved to be better than the existing keyword-based search.
However, in the case of using the ranking scheme of the semantic relationships, the diversity of the semantic relationships must be considered to ensure a more accurate search. For example, the sentences ‘interested in a topic’ and ‘write a publication about a topic’ each have a different importance in describing or explaining a person. Namely, ‘write’ is a more detailed and informative descriptor. In other words, the diversity of the semantic relationship between a resource a particular keyword means that the semantic relationships between a resource and a keyword have a different importance in determining a resource relevant score with respect to a particular keyword.
In this respect, however, the scheme proposed in relevant research 1 does not consider the diversity of the semantic relationships, resulting in low search accuracy. Also, the scheme proposed in relevant research 2 is disadvantageous in that a domain expert manually (or passively) assigns a weight value according to the diversity of the semantic relations, so it is impractical to be applied to a complicated, large ontology. In addition, the above-described related arts have the shortcomings in that they cannot effectively handle a query consisting of one or more keywords with different importance.